Autoradiographic distribution of binding sites for the non-NMDA receptor antagonist CNQX in chick brain.

The anatomical distribution of binding sites for the non-N-methyl-D-aspartate (non-NMDA) glutamate receptor antagonist [3H]6-cyano-7-nitroquinoxaline-2,3-dione ([3H]CNQX) in 1-day-old chick brain was investigated. Specific [3H]CNQX binding sites were widely distributed but were particularly densely localised in the molecular layer of the cerebellum. In the midbrain, the binding was comparatively low, except for relatively high levels in the nucleus isthmi of the optic lobe. The distribution of [3H]CNQX binding was markedly different to that of the NMDA receptor ligand [3H]MK-801. Overall, the localisation of [3H]CNQX binding was similar to the combined distributions of [3H]AMPA and [3H]kainate binding sites. Kainate inhibited [3H]CNQX binding throughout the brain. AMPA also inhibited [3H]CNQX binding in the fore- and midbrain, but the dense binding in the molecular layer of the cerebellum was notable in being AMPA-insensitive.